Ultralight aviation is the flying of lightweight, 1- or 2-person fixed-wing aircraft, also called microlight aircraft in the UK, India and New Zealand. Some countries differentiate between weight shift and 3-axis aircraft, calling the former “microlight” and the latter “ultralight”.

During the late 1970s and early 1980s, mostly stimulated by the hang gliding movement, many people sought affordable powered flight. As a result, many aviation authorities set up definitions of lightweight, slow-flying aeroplanes that could be subject to minimum regulations. The resulting aeroplanes are commonly called “ultralight aircraft” or “microlights”, although the weight and speed limits differ from country to country. In Europe the sporting (FAI) definition limits the maximum take-off weight to 450 kg (992 lb) and a maximum stall speed of 65 km/h (40 mph). Such a definition forces the aircraft to be capable of a slow landing speed and short landing roll in the event of an engine failure.

There is also an allowance of a further 10% on Maximum Take-off Weight for seaplanes and amphibians, and some countries (such as Germany,Poland and France) also allow another 5% for installation of a ballistic parachute.

The safety regulations used to approve microlights vary between countries, the strictest being in the United Kingdom, Italy, Sweden and Germany, while they are almost non-existent in France and the United States. The disparity between regulations can be a barrier to international trade and overflight in strict regions, as is the fact that these regulations are invariably sub-ICAO, which means that they are not internationally recognised.

In most affluent countries, microlights or ultralight aircraft now account for a significant percentage of the global civilian-owned aircraft. For instance in Canada in October 2010, the ultralight aircraft fleet made up to 19% of the total civilian aircraft registered. In other countries that do not register ultralight aircraft, like the United States, it is unknown what proportion of the total fleet they make up. In countries where there is no specific extra regulation, ultralights are considered regular aircraft and subject to certification requirements for both aircraft and pilot.